The present invention relates to a light-emitting device using a clad layer consisting of asymmetric units, and, more particularly, to a light-emitting device using a clad layer consisting of asymmetric units, wherein the clad layer is provided by repeatedly stacking a unit having an asymmetric energy bandgap on upper and lower portions of an active layer, and the inflow of both electrons and holes into the active layer is arbitrarily controlled through the clad layer, so that the internal quantum efficiency can be improved.
As illustrated in FIG. 1, a light-emitting device is basically composed of an n-type semiconductor layer 10 providing electrons, a p-type semiconductor layer 20 providing holes, and an active layer 30 emitting light by combining electrons and holes.
In order to improve the light-emitting performance of this light-emitting device, it is necessary to maximize its internal quantum efficiency (IQE). The IQE refers to the number of photons compared to the number of recombined electrons. A characteristic that allows the electrons and holes to flow into the active layer 30 upon the application of a voltage, a characteristic that effectively confines the electrons and holes in the active layer 30, a characteristic that recombines the electrons and holes in the active layer 30, and so on should be generally considered to improve the IQE.
The prior arts suggest a method for forming an electron blocking layer (EBL) having a large energy bandgap between an active layer and a p-type semiconductor layer and a method for forming a symmetric superlattice layer as a clad layer between an active layer and an n-type semiconductor layer and between the active layer and a p-type semiconductor layer so as to improve the IQE.
The method for forming the EBL is to ultimately improve the recombination rate of electrons and holes in the active layer by confining the electrons in the active layer by preventing the electrons which have flowed from the n-type semiconductor layer into the active layer from moving to the p-type semiconductor layer. However, although this method has an advantage that prevents the electrons from moving to the p-type semiconductor layer due to the EBL's conduction band discontinuity, it also has a disadvantage that limitedly improves the IQE because the holes having a larger mass than the electrons cannot flow into the active layer due to the EBL's valence band discontinuity. FIG. 2 illustrates an energy bandgap of a light-emitting device having an EBL 21 provided between an active layer and a p-type semiconductor layer. As can be seen, the EBL 21 prevents the movement of electrons so that the electrons can be confined in the active layer but also prevents holes from smoothly flowing into the active layer.
Next, the method for forming the symmetric superlattice layer on upper and lower portions of the active layer has an advantage that improves the inflow of holes from the p-type semiconductor layer through a miniband defined by the superlattice layer but has a disadvantage that cannot effectively prevent electrons which have flowed into the active layer from moving to the p-type semiconductor layer. FIG. 3 illustrates an energy bandgap of a light-emitting device having a symmetric superlattice layer provided on upper and lower portions of an active layer. As can be seen, the superlattice layer improves the inflow of holes but cannot prevent the outflow of electrons from the active layer.